The Insulated-Gate Bipolar Transistor (IGBT) is a three-terminal power semiconductor device primarily used as an electronic switch and in newer devices is noted for combining high efficiency and fast switching. It switches electric power in many modern appliances such as: Variable-Frequency Drives (VFDs), electric cars, trains, variable speed refrigerators, lamp ballasts, air-conditioners, and even stereo systems with switching amplifiers.
IGBTs are often used for high voltage (e.g., greater than 600V) and high-current power converter applications. In these types of applications, a short-circuit of the load wire to a power source will result in a large current flowing through the IGBT, which is likely to damage the IGBT. Because of the potential for damage to IGBTs, gate drive circuits must detect IGBT short-circuit conditions and turn off the IGBT safely to prevent damage to the IGBT.
Desaturation, also referred to herein as “DESAT”, detection is a technique used to determine whether a transistor (e.g., an IGBT or Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) is operating in a fully turned on condition. If the transistor is only partially turned on or in a DESAT condition, there is the possibility for the device to overheat and self destruct.
A DESAT condition may be caused by a number of events such as: excessive current; incorrect gate drive; or other faults in the transistor. To prevent such conditions and to avoid permanent damage to the transistor, it is important that the DESAT condition be detected and preventative action be taken in a timely manner.